How Many Systems In That Galactic Empire Now?

How many of the planets in our galaxy might support life? According to the latest estimates by a group of Danish and Australian researchers, habitable planets number in the billions.

According to Danish and Australian researchers who used an improved version of a 250-year old theory (The Titius-Bode law), there are billions of the stars in the Milky Way located in the “habitable zone”, where liquid water might exist, and with it, life as we know it.

For a planet to have liquid water — something necessary to support life as we know it — it has to be within a certain distance of its star. Too close, and the water burns up. Too far away, and it’s a frozen wasteland.
By using the Kepler telescope, astronomers have discovered over a thousand exoplanets in our galaxy. Most of the planetary systems discovered have 2-6 planets, but because Kepler is only suitable for discovering planets near their star, many others might lie undiscovered...

The calculations show that billions of the stars in the Milky Way will have one to three planets in the habitable zone, where there is the potential for liquid water and where life could exist.

Science fiction fans the 1950's may have felt that Isaac Asimov was exaggerating when he described the mighty galactic empire:

And in the center of an open cluster of ten thousand stars, whose light tore to shreds the feebly encircling darkness, there circled the huge Imperial planet, Trantor.

But it was more than a planet; it was the living pulse-beat of an Empire to twenty million stellar systems...